1. Field of the Invention
In photochemical reactions, the course of the reaction can be affected by the excited state from which the product is formed. The excited state is determined initially by the energy absorbed by the molecule, but the initial state may be changed by interaction with the molecule's environment. Singlet and triplet states are the common photochemical excited states, which may be achieved by either direct absorption of energy or by use of a sensitizer.
The reaction product can depend on the excited state from which the reaction product is derived, not only as to isomer, but also in some cases as to structure, such as cyclizations. Therefore, where the possibility exists for two different products to be obtained, depending on the nature of the excited state, a quencher may be employed to dissipate the energy of one of the excited states in a manner which does not result in product formation.
Quenchers also find use in the study of photochemical reactions. In order to ascertain whether a particular product is formed through a triplet or singlet state, a quencher may be employed which will prevent the reaction from going through a triplet state. In this manner, if the reaction proceeds in the presence of the quencher, assuming the quencher has the appropriate triplet energy value (E.sub.T), then the triplet state of the reactant must be very short lived or the reaction must proceed by means of a singlet state. The lower the triplet energy value for the molecule which is undergoing reaction, the lower the triplet energy value required for the quencher. Therefore, quenchers with low triplet energy values can be quite valuable in being able to quench reactions which occur at relatively low energy values. However, the quencher must not absorb the exciting light as this would inhibit the photochemical reaction. Ideal quenchers, therefore, have high singlet energies and low triplet energies.
2. Description of the Prior Art
A list of quenchers may be found in the 1971 J. T. Baker catalog. The description of the use of quenchers may be found in Turro, "Molecular Photochemistry", Benjamin, New York, 1967. The reaction of 1,2-bis(hydroxylamino) tetramethylethane is reported to give a 1-oxylaziridine in Luckhurst et al., Tetrahedron Letters, 675 (1971).